A. Field of the Invention
This invention relates to apparatus for the production of particulate coke stock and distillate stock from heavy petroleum residiums which have previously been economically unattractive for recovery and refining. The increasing price of fuel products and world fuel shortages have made it imperative to produce fuels from these sources.
Heavy petroleum residiums are refined by passing the residiums through a fluid coker apparatus which consists essentially of a reactor vessel and a burner vessel. The residum is sprayed into the interior of the reactor vessel from a plurality of points. The interior of the reactor vessel is supplied with a fluidized bed of particulate coke which is maintained at elevated temperatures. The residium contacts this hot coke and is broken into volatile fractions and non-volatile fractions. The volatile fraction rises to the surface of the fluidized bed of coke and is passed through a separatory and fractionating apparatus at the top of the reactor vessel. The separatory apparatus scrubs the volatile fraction and removes particulate material before passing the volatile fraction to the fractionating apparatus. The volatiles are condensed in this latter section and are removed from the reactor as distillate stock. The distillate stock can be refined into various grades of motor fuels, but that aspect of the refinement process does not constitute a part of the present invention.
The non-volatile fraction of the contacted residium condenses on the hot, particulate coke in the fluidized bed of the reactor vessel. The non-volatiles coat the coke particles with a new and increasing dimension of coke product. The coke particles grow in size from an original "seed" particle size, as they are introduced to the reactor vessel initially, to a maximum fluid coke size, as they achieve upon being coated with non-volatile residium product. The maximum particle size can vary and is set by calibration of the discharge line from the reactor vessel, wherein a separatory device, such as a cyclone separator will distinguish between particles of coke which have "grown" or achieved the maximum dimension and those that have not achieved that dimension. Under-sized particles are returned to the fluidized bed of the reactor vessel for further treatment, while coke particles of the maximum desired size are discharged to the burner vessel of the fluid coker apparatus, or directly to storage.
The burner vessel is a second fluidized bed of particulate coke. This fluidized bed is maintained several hundred degrees in temperature above the bed of the reactor vessel. It is kept at such elevated temperatures (1000 F.-1500 F.) by the combustion of a portion of the particulate coke feed in its fluidized bed. This combustion is initiated by an auxiliary burner which supplies heated gases at initial start up of the fluid coker apparatus, but burner vessel temperatures are thereafter maintained simply by providing a combustion supporting gas, such as air, to the already hot particulate coke in the fluidized bed of the burner vessel.
Some of the hot combusted coke particles are metered back to the reactor vessel to complete the cyclic flow of coke to and from the reactor vessel and the burner vessel and to maintain the residium coking temperatures in the reactor vessel. The remaining surplus of particulate coke is discharged from the top of the fluidized bed of the burner vessel and quenched with a coolant, such as water, before being transported to a storage facility. The structure and arrangement of the burner vessel is of critical importance to the operation of the fluid coking apparatus in light of the extremely high temperatures maintained in the burner vessel, the corrosive, oxidative conditions inherent in such a vessel and the need to maintain a calibrated flow of particulate coke through the vessel. In addition, the operation of the apparatus should maximize its economical operation in order to maintain the favorable recovery of the residium raw stock.
The subject apparatus may also find application as a regenerator for a catalytic cracking unit which combusts the coke coated upon the catalyst particulate in a fluidized bed.
B. The Prior Art
The prior art has provided operational fluid coking devices of acceptable capability in which a circulating flow of coke is maintained between a reactor vessel and a burner vessel. However, the prior art burner vessels have not maximized the efficiency of said apparatus with respect to volume and materials used in the burner vessel.
In U.S. Pat. No. 2,881,130 to Pfeiffer et al. a fluid coker apparatus is shown which has a burner vessel of generally cylindrical design. The entire lower portion of the vessel contains the fluidized bed, which subjects the various stand pipes to the aggressive environment of the bed. The vessel has a generally conical bottom head or floor. In addition, the fluidizing fuel-air delivery pipe has only a central discharge point.
In U.S. Pat. No. 2,881,133 to Whiteley et al. a similar fluid coker apparatus is described. Again, the burner vessel has a deep conical bottom head or floor, and the standpipes are directly in contact with the fluidized bed without additional support. The air discharge and fluidization inlet has only a central, covered discharge port.
These characteristics of the prior art provide limitations on the efficient, economical operation of a burner vessel in a fluid coker apparatus in which only nominally recoverable residiums are processed. With a view toward improving on the efficiency and economy of the prior art burner vessels of fluid coker apparatus and the production of profitable residium products, the present invention contemplates several novel advances in burner vessel design which provide efficient, economical operation.